The invention concerns a process for the production of water-soluble, naturally folded and secreted polypeptides after expression in prokaryotic cells.

Protein synthesis in prokaryotic organisms, which is also called translation, takes place on the ribosomes in the cytoplasm. When recombinant DNA is expressed in prokaryotic host organisms, it is often desirable to secrete the recombinant gene product or protein that is obtained in this process from the cytoplasm through the inner bacterial membrane into the periplasmic space between the inner and outer membrane. Secreted proteins can then be released from the periplasm into the nutrient medium for example by osmotic shock. A disadvantage of this process is that the secreted polypeptides often do not form the native, biologically active conformation (Hockney, TIBTECH 12 (1994) 456 - 463; Baynex, Curr. Opin. Biotechnol. 10 (1999) 411-421).

Recently molecular chaperones and folding catalysts such as peptidyl-prolyl-cis/transisomerases or protein disulfide isomerases (Glockshuber et al., EP-A 0 510 658) have been used to increase the yield of native recombinant protein when folded in vivo (Thomas et al., Appl. Biochem. Biotechnol. 66 (1997) 197-238). In some cases this has led to considerable improvements in the expression e.g. of ribulose bisphosphate carboxylase (RUBISCO; Goloubinoff et al., Nature 337 (1989) 44-47), human procollagenase (Lee & Olins, J. Biol. Chem. 267 (1992) 2849-2852) or neuronal nitrogen oxide synthase from rats (Roman et al., Proc. Natl. Acad. Sci. USA 92 (1995) 8428-8432). In these examples GroEL/ES or the DnaK system from E. coli was co-overexpressed in the cytosol. The positive effect is usually an increased yield of the desired protein in a soluble form.

The co-expression of chaperones has also been examined when recombinant proteins are secreted into the periplasm of E. coli. However, in this case only a cytosolic overexpression of chaperones was evaluated in order to optimize secretion into the periplasm (Perez-Perez et al., Biochem. Biophys. Res. Commun. 210 (1995) 524-529; Sato et al., Biochem. Biophys. Res. Commun. 202 (1994) 258-264; Berges et al., Appl. Environ. Microbiol. 62 (1996) 55-60). Previous attempts at cosecretion in E. coli have only concerned folding catalysts such as e.g. protein disulfide isomerase (PDI; Glockshuber et al., EP-A 0 510 658) or peptidylprolyl-cis/trans-isomerases or Dsb proteins from E.coli (Knappik et al., Bio/Technology 11 (1993) 77-83; Qiu et al., Appl. Environm. Microbiol. 64 (1998) 4891-4896 and Schmidt et al., Prot. Engin. 11 (1998) 601 - 607). Recently, co-overexpression of the periplasmic Skp protein led to more efficient folding of phase display and higher yield of antibody fragments secreted to the periplasm (Bothman and Plückthun, Nat. Biotechnol. 16 (1998) 376-380; Hayhurst and Harris, Prot. Expr. Purif. 15 (1999) 336-343).

Compounds such as urea or urea derivatives, formamide, acetamide or L-arginine are used in methods for the in vitro renaturation of insoluble protein aggregates (inclusion bodies) which are formed during the cytoplasmic expression of recombinant DNA in prokaryotic cells. L-arginine as an additive can considerably improve the yield of natively folded proteins in the renaturation in vitro (Rudolph et al., US-Patent No. 5,593,865; Buchner & Rudolph, Bio/Technology 9 (1991)157-162; Brinkmann et al., Proc. Natl. Acad. Sci USA 89 (1992) 3075-3079; Lin & Traugh, Prot. Express. Purif. 4 (1993) 256-264 ; EP 725140).

The object of the invention is to provide a process for the production of water-soluble, naturally folded eukaryotic polypeptides after expression in prokaryotes which can be carried out in a simple manner and which does not require a laborious in vitro aftertreatment such as solubilization, reduction and renaturation of inclusion bodies, reduction and renaturation.

The object is achieved by a process for the production of a water-soluble, naturally folded eukaryotic polypeptide containing two or several cysteines linked by disulfide bridges, by culturing prokaryotic cells,

1. a) in which the said prokaryotic cells contain an expression vector which encodes the said polypeptide which contains a prokaryotic signal sequence at the N-terminus,
2. b) under conditions under which the polypeptide is secreted into the periplasm or the medium,
3. c) cleaving the signal sequence and isolating the polypeptide from the periplasm or the medium

• R and R₁ represent hydrogen or a saturated or unsaturated branched or unbranched C₁-C₄ alkyl chain and
• R₂ represents hydrogen, NHR₁ or a saturated or unsaturated branched or unbranched C₁ - C₃ alkyl chain, wherein the concentration of arginine or of the compound of general formula I is at least 0.1 mol/L.

The concentration of arginine or of the compound of the general formula I is at least 0.1 mol/l, but can also be considerably higher provided the solubility of arginine or the said compound is ensured. Arginine or the compounds of the general formula I are preferably used at a concentration of 0.1 to 1.5 mol/l.

Formamide, acetamide, urea or urea derivatives such as ethylurea or methylurea are preferably added as compounds of the general formula I, to the nutrient medium that is used to culture the prokaryotic cells. Arginine can for example be used as the hydrochloride or as another titrated form of the arginine base. However, L-arginine is preferably used and the hydrochloride form of L-arginine is particularly preferred.

In a preferred embodiment of the process according to the invention, reducing thiol reagents which contain SH groups are additionally added to the nutrient medium (fermentation medium) used to culture the prokaryotic cells which further increases the yield of recombinantly produced protein. 0.1 - 15 mmol/l thiol reagent is preferably added. According to the invention the term "thiol reagent" either means a reducing (reduced) reagent with SH groups or a mixture of reducing reagents with SH groups and oxidizing reagents with disulfide groups. Preferred substances are reduced and oxidized glutathione (GSH), cysteine, cystine, N-acetylcysteine, cysteamine, β-mercaptoethanol and similar compounds. The thiol reagents can be used singly as well as in mixtures. Thiol reagents such as glutathione (GSH) which have a single SH group per molecule are particularly suitable. Thiol reagents such as glutathione are known to improve the yield of natively folded proteins when recombinant DNA is expressed in prokaryotic cells (Glockshuber et al., EP-A 0 510 658).

In a further preferred embodiment of the process according to the invention molecular chaperones are additionally overexpressed and cosecreted. Chaperones are understood according to the invention as proteins which protect other non-native proteins from aggregation in vivo and promote the formation of their native conformation. Molecular chaperones are used in the prior art to stabilize proteins and thus to protect them from aggregation and inactivation (Buchner et al., EP-A 0 556 726 A1). Preferably ATP-dependent chaperones of the HSP40 type (molar mass ca. 40 kDa) or a small heat shock protein (sHSP) are preferably used. DnaJ is a 40 kDa heat shock protein which occurs in the cytoplasm of E. coli and is a part of the so-called Hsp70 chaperone system (Bukau, B. & Horwich, A., Cell 92 (1998) 351-366). DnaK (Hsp70) and GrpE also belong to this system. Particular proteins are folded into the native conformation by the DnaK system in an ATP-dependent process (Schröder et al., EMBO J. 12 (1993) 4137-4144; Langer et al., Nature 356 (1992) 683 - 689). DnaJ protects non-native proteins from aggregation in the absence of DnaK and ATP and mediates a folding-competent state (Schröder et al., EMBO J. 12 (1993) 4137-4144). It has been shown that the co-expression of DnaJ in the cytosol can lead to an increase in the yield of soluble protein (Yokoyama et al., Microbiol. Ferment. Technol. 62 (1998) 1205-1210). The co-secretion of an N-terminal fragment of DnaJ which comprises the amino acids 1-108 and in the following is referred to as the J domain (Kelley, TIBS 23 (1998) 222-227) is additionally preferred. The J domains and a G/F-rich domain which are responsible for interactions with DnaK are located in this region (Wall et al., J. Biol. Chem. 270 (1995) 2139-2144). WO9818946 describes a process for producing heterologous polypeptides in bacteria wherein both the heterologous polypeptide and the molecular chaperons, DsbA or DsbC, are secreted into the periplasm of the bacteria. In a further process the heterologous protein is isolated from the periplasm or the medium using a chaotropic agent such as urea. EP885967 discribes a method for producing a heterologous protein in procaryotes by cotransformation of DnaJ and recovering said heterologous protein from the culture medium.

Hsp25 (e.g. from the mouse) is a representative of the small heat shock proteins (Gaestel et al., Eur. J. Biochem. 179 (1989) 209-213) which are a ubiquitous class of chaperones. The molar mass of these proteins is between 15 and 30 kDa. During heat shock there is a substantial accumulation of sHsps in the cell (up to 1% of the total cell protein - Arrigo & Landry (1994), In Morimoto (Hrsg.): The Biology of Heat Shock Proteins and Molecular Chaperones, Cold Spring Harbour Press, 335-373). Like DnaJ proteins, sHsps have the property of preventing the aggregation of non-native proteins and of keeping these in a folding-competent state (Jakob et al., J. Biol. Chem. 268 (1993) 1517-1520; Ehrsperger et al., EMBO J. 16 (1997) 221-229).

The term overexpression" according to the present invention means an increase of the expression of secreted proteins such as e.g. DnaJ and Hsp25 (preferably by at least 100 %) compared to expression in the wild-type of the respective prokaryotic host organism. Such an overexpression can for example be achieved when the genes (for the protein, chaperone and/or signal peptide) are under the control of a strong prokaryotic, preferably inducible, expression signal (e.g. of a lac or T7 promoter or a derivative thereof).

The secretion construct for the overexpression of polypeptides (proteins) including regulatory regions (promoter and terminator) on the recombinant DNA is preferably integrated into a vector which additionally encodes the arginine-tRNA _AGA/AGG which is rare in prokaryotes or it is co-expressed with a vector which encodes this tRNA (Brinkmann et al., Gene 85 (1989) 109-114). This enables the co-overexpression of the respective proteins into the bacterial periplasm as well as the trancription of the rare tRNA^Arg_AGA/AGG, which often results in an increased synthesis of the desired protein in the bacterial host organism.

A prokaryotic signal sequence in the sense of the invention is understood as a nucleic acid fragment which is derived from prokaryotes, preferably from gram-negative bacteria, and ensures that proteins bound to the signal peptide can penetrate through the inner bacterial membranes. As a result the proteins are located in the periplasm or in the cell supernatant. Such signal sequences usually have a length of 18 - 30 amino acids and are described for example in Murphy & Beckwith: Export of Proteins to the Cell Envelope in Escherichia coli in Neidhardt et al. (editors): Escherichia coli and Salmonella, Second Edition, Vol. 1, ASM Press, Washington, 1996, p. 967-978. The cleavage of bacterial signal sequences can for example occur after an Ala-X-Ala sequence (von Heijne et al., J. Mol. Biol. 184 (1985) 99-105). The structure of the bacterial signal peptidase is described in Paetzel et al., Nature 396 (1998) 186-190. Signal sequences are preferably used that are cleaved again from the desired protein by proteases located in the periplasm of prokaryotic cells. Alternatively such proteases can be added to the cell supernatant or to the isolated protein to cleave the signal sequence.

The process according to the invention can improve the heterologous expression of numerous eukaryotic proteins such as e.g. proteases, interferons, protein hormones, antibodies or fragments thereof. The process is particularly suitable for the heterologous production of proteins which contain at least two cysteines linked by a disulfide bridge in their native state, especially when they have no prokaryotic signal sequence fused at the N-terminus and insoluble inclusion bodies are formed during their prokaryotic expression. The process is particularly suitable for proteins which contain more than 5 disulfide bridges in the native state. Such a protein is for example a recombinant plasminogen activator (referred to as rPA in the following, Martin et al., Cardiovasc. Drug Rev. 11 (1993) 299-311, US-Patent Nr. 5,223,256). rPA has 9 disulfide bridges which are not formed in the reducing cytosol of E. coli.

The periplasmic location of the protein and optionally of the chaperone is ensured by operative linkage with a signal peptide to penetrate the inner bacterial membranes.

A concentration of 0.4 mol/l L-arginine and 5 mmol/l glutathione (in the case of co-secretion of DnaJ, J domain, Hsp25 and scFv) or 0.4 mol/l L-arginine without glutathione (without co-secretion of DnaJ) has proven to be optimal for the expression of such a plasminogen activator.

In order to isolate the secretory rPA protein in a functional form in E coli, the gene for this protein from the plasmid pA27fd7 (Kohnert et al., Protein Engineering 5 (1992) 93-100) was fused by genetic engineering methods to a prokaryotic signal sequence of gram-negative bacteria, for example to the signal sequence of pectate lyase B (PelB) from Erwinia carotovora. The gene fusion was constructed by cloning into the vector pET20b(+) (Novagen Inc., Madison, USA). As a result the gene expression is under the control of the T7 promoter. The signal sequence present in the fusion protein mediates the secretion into the periplasm. The signal sequence is cleaved during or after the secretion by a peptidase located at the inner membrane. The secreted protein can then fold in the periplasm. The oxidizing conditions in this compartment enable the formation of disulfide bridges (Wuelting and Plückthun, Mol. Microbiol. 12 (1994) 685-692). The inventive addition of low molecular weight additives that improve folding and thiol reagents in the nutrient medium and the simultaneous co-overexpression of DnaJ, J-domain or Hsp25 in the periplasm enables the yield of functional protein to be increased by more than 100-fold.

Other examples of polypeptides according to the invention are antibodies or antibody fragments such as single-chain F_v-fragment (scFv, e.g against thyroid stimulating hormone, TSH). ScF_vs are shortened antibodies which are only composed of the variable sections (F_v) of the heavy and light chain of an antibody which are artificially fused via a short peptide linker (usually Gly₄Ser₃) (Hudson, Curr. Opin Biotechnol. 9 (1998) 395-402). ScF_vs normally have the same affinity for the antigen as the paternal F_v-strands, but can be overexpressed in E coli. Since they have stabilizing intradomain disulfide bridges which are essential for stability, an expression in the cytosol usually leads to the formation of inclusion bodies (Shibui et al., Appl. Microbiol. Biotechnol. 37 (1992) 352-357). ScF_vs can be specifically optimized for binding the desired antigens by random mutations and subsequent phage display selection (Allen et al., TIBS 20 (1995) 511-516; Hoogenboom et al., Immunotechnology 4 (1998) 1-20). Addition of 5 mM GSH and 0.4 M L-arginine enables the yield of functional ScF_v-TSH to be improved 7-fold in the periplasm and by 43-fold in the medium supernatant compared to a culture without additives.

The following examples, publications, the sequence protocol and the figures further elucidate the invention, the protective scope of which results from the patent claims. The described methods are to be understood as examples which still describe the subject matter of the invention even after modifications.

• SEQ ID NO: 1 and 2 show the sequence of the part of the expression plasmid pUBS520-pIN-dnaJ which encodes the fusion protein composed of the OmpA signal sequence and DnaJ together with the regulatory sequences (promoter, terminator) which were amplified from pIN III ompA3-dnaJ.
• SEQ ID NO: 3 and 4 show the sequence of the part of the expression plasmid pUBS520-pIN-J-domain which encodes the fusion protein composed of the OmpA signal sequence and J domain together with the regulatory sequences (promoter, terminator) which were amplified from pIN III ompA3-dnaJ.
• SEQ ID NO: 5 and 6 show the sequence of the part of the expression plasmid pUBS520-pIN-hsp25 which encodes the fusion protein composed of the OmpA signal sequence and Hsp25 together with the regulatory sequences (promoter, terminator) which were amplified from pIN III ompA3-hsp25.
• SEQ ID NO: 7 and 8 show the sequence of the part of the expression plasmid pUBS520-scFvOx which encodes the fusion protein composed of the PelB signal sequence and scFvOxazolon together with the regulatory sequences (promoter, terminator) which were amplified from pHEN-scFv or pIN III ompA3.
• SEQ ID NO: 9 and 10 show the sequence of the part of the expression plasmid pET20b(+)-rPA which encodes the fusion protein composed of PelB signal sequence and rPA.

• Fig. 1 shows the dependency of the expression of native rPA in the periplasm of E. coli with 5 mM GSH on the L-arginine concentration and various co-secretion constructs.
• Fig. 2 shows a comparison of the expression of rPA in the periplasm of E. coli BL21(DE3) when co-secreted with DnaJ and when 5 mM GSH and various low molecular substances that improve folding are added to the medium.
• Fig. 3 shows a schematic representaion of the expression plasmid pUBS520-pIN-dnaJ.
• Fig. 4 shows a schematic representaion of the expression plasmid pUBS520-pIN-J-Domain.
• Fig. 5 shows a schematic representaion of the expression plasmid pUBS520-pIN-hsp25.
• Fig. 6 shows a schematic representaion of the expression plasmid pUBS520-scFvOx.
• Fig. 7 shows a schematic representation of the expression plasmid pET20b(+)-rPA.
• Fig. 8 shows the dependency of the expression of functional scFv-TSH on the concentration of L-arginine in the presence of 5 mM GSH in the periplasm and in the culture medium.

For the periplasmic overexpression of DnaJ, the J-domain and Hsp25 in E. coli, the DNA which encodes these proteins was fused by genetic engineering to the signal sequence of the outer membrane protein A (OmpA) of E. coli and the fusion was expressed in E. coli on a recombinant plasmid under the control of the lac-lpp promoter. As a result the polypeptide chains of DnaJ and Hsp25 are transported into the periplasm of the prokaryotic host organism and are natively folded there. Their location and native folding was demonstrated by limited proteolysis with trypsin and by Western blot.

Molecular genetic techniques were based on Ausubel et al. (ed.), J. Wiley & Sons, 1997, Curr. Protocols of Molecular Biology. Oligonucleotides were obtained from the companies MWG Biotech, Ebersberg or GIBCO Life Sciences, Eggenstein, DE.

The gene which encodes DnaJ, Gene Bank Accession No. M 12565, was amplified by PCR and cloned by means of the thereby generated restriction cleavage sites EcoRI and BamHI into the expression plasmid pIN III ompA3 (Ghayreb et al., EMBO J. 3 (1984) 2437-2442. The sequence of the cloned PCR fragment was confirmed by dideoxy sequencing (LiCor DNA-Sequencer 4000, MWG Biotech, Ebersberg). The resulting plasmid was named pIN III ompA3-dnaJ. The sequence of DnaJ expressed in the periplasm differs from that of the wild-type protein in that the polypeptide sequence begins with Gly-Ile-Pro instead of Met, hence there was an N-terminal extension of 2 amino acids. Hence DnaJ is under the control of the lac-lpp promoter which is induced with IPTG (isopropyl-β-D-thiogalactoside).

The region from the plasmid pIN III ompA3-dnaJ which encodes the lac-lpp operon, the signal sequence, the dnaJ gene and the terminator region of the operon was amplified by means of PCR (SEQ ID NO: 1). The PCR product was cleaved with the restriction endonuclease BglII and cloned into the vector pUBS520 linearized with the restriction endonuclease BamHI. The resulting plasmid was named pUBS520-pIN-dnaJ (Fig. 3).

Two stop codons were inserted in the plasmid pUBS 520-pIN-dnaJ after the nucleotide 324 by means of the QuikChange mutagenesis system (Promega, Mannheim, DE) so that only the first 108 amino acids are expressed. The sequence of the mutagenized region was determined by dideoxy sequencing (LiCor DNA-Sequencer 4000, MWG Biotech, Ebersberg) and the expression of the shortened protein fragment was detected by Western blotting and detection with an anti-DnaJ antibody. The plasmid that was formed was named pUBS 520-pIN-J-domain (Fig. 4).

The gene which encodes Hsp25, Gene Bank Accession No.: L 07577, was amplified by PCR and cloned by means of the thereby generated restriction cleavage sites EcoRI and BamHI into the expression plasmid pIN III ompA3 (Ghayreb et al., EMBO J. 3 (1984) 2437-2442). The sequence of the cloned PCR fragment was checked by dideoxy sequencing (LiCor DNA-Sequencer 4000, MWG Biotech, Ebersberg). The resulting plasmid was named pIN III ompA3-hsp25. The sequence of the Hsp25 expressed in the periplasm differs from that of the wild-type protein in that the polypeptide sequence begins with Gly-Ile-Leu instead of Met, hence there was an N-terminal extension of 2 amino acids. Hence Hsp25 is under the control of the lac-lpp promoter which is induced with IPTG (isopropyl-β-D-thiogalactoside).

The region from the plasmid pIN III ompA3-hsp25 which encodes the lac-lpp operon, the signal sequence, the hsp25 gene and the terminator region of the operon was amplified by means of PCR (SEQ ID NO: 5). The PCR product was cleaved with the restriction endonuclease BglII and cloned into the vector pUBS520 linearized with the restriction endonuclease BamHI. The resulting plasmid was named pUBS520-pIN-hsp25 (Fig. 5).

The co-expression of a single chain Fv fragment which is directed against the hapten oxazolon (scFvOxazolon; Fiedler and Conrad, Bio/Technology 13 (1995) 1090-1093) which has no chaperone properties was examined as a negative control.

The region from the plasmid pHEN-scFvOx which encodes the lac promoter, the signal sequence pelB and the scfvox gene was amplified by means of PCR. The region from the plasmid pIN III ompA3 which encodes the lpp termintor was amplified in a second PCR. The two fragments were fused in a subsequent PCR. The PCR product (SEQ ID NO: 7) that was formed in this manner was cleaved with the restriction endonuclease BglII and cloned into the vector pUBS520 that was linearized with the restriction endonuclease BamHI. The resulting plasmid was named pUBS520-scFvOx (Fig. 6).

The gene of a plasminogen activator (rPA) from the plasmid vector pA27fd7 (Kohnert et al., Protein Engineering 5 (1992) 93-100) was amplified with the aid of a PCR method. The PCR product was cleaved with the restriction endonucleases NcoI and BamHI and cloned into the plasmid vector pET20b(+) (Novagen Inc., Madison, USA). The plasmid encodes a fusion protein which is composed of the signal sequence of PelB (pectate lyase from Erwinia carotovora) and rPA and the secretion of rPA into the periplasm was checked by dideoxy sequencing (LiCor DNA-Sequencer 4000, MWG Biotech, Ebersberg, DE). The construct was named pET20b(+)-rPA (Fig. 7). rPA is expressed from the plasmid under the control of the T7 promoter, the T7-RNA-polymerase in the strain E. coli BL21(DE3) being under the control of the lacUV5 promoter. The induction was carried out by adding IPTG.

The rPA expressed in the periplasm differs from the plasminogen activator described by Kohnert et al. in that the second amino acid (Ser) is substituted by Ala.

A stationary overnight culture of E. coli BL21(DE3) (Studier & Moffat, J. Mol. Biol. 189 (1986) 113-130) which had been transformed with pET20b(+)-rPA and pUBS520-pIN-dnaJ (co-secretion of DnaJ), an overnight culture of E. coli BL21(DE3) which had been transformed with pET20b(+)-rPA and pUBS520-pIN-J-domain (co-secretion of the J-domain), an overnight culture of E. coli BL21(DE3) which had been transformed with pET20b(+)-rPA and pUBS520-pIN-hsp25 (co-secretion of Hsp25), an overnight culture of E. coli BL21(DE3) which had been transformed with pET20b(+)-rPA and pUBS520-scFvOx (co-secretion of scFvOx), an overnight culture of E. coli BL21(DE3) which had been transformed with pET20b(+)-rPA and pUBS520 or an overnight culture of E. coli BL21(DE3) which had been transformed with pET20b(+) and pUBS520 (control culture), was diluted in a ratio of 1:50 in 100 ml LB-Medium containing ampicillin (100 µg/ml) and kanamycin (50 µg/ml, Fluka Chemica, Neu-Ulm, DE) and shaken at 24°C and 170 rpm. After 3 h growth, 5 ml aliquots of the culture were added to 10 ml LB medium containing the aforementioned amounts of ampicillin and kanamycin and various concentrations of GSH (0-10 mM, Fluka, DE) and L-arginine HCl (0-0,4 M, ICN) and each was induced with 1mM IPTG (isopropyl-β-D-thiogalactoside, AppliChem, Darmstadt, DE). The cells were shaken for a further 21 h at 24°C and 170 rpm and a 1 ml sample was taken after determining the OD₆₀₀. These 1 ml cell samples were fractionated in 2 ml Eppendorf reaction vessels by a modified protocol according to Jacobi et al. (J. Biol. Chem. 272 (1997) 21692-21699). In detail 500 µl fractionation buffer (150 mM NaCl (Roth GmbH), 50 mM Tris/HCl (Roth GmbH), 5 mM EDTA (Biomol) and 1 mg/ml polymyxin B sulfate (Sigma), pH 7.5) was added to the cell pellet, shaken for 1 h at 10 °C on an Eppendorf thermoshaker at 1400 rpm and then centrifuged for 15 min at 14 000 rpm in an Eppendorf microcentrifuge cooled to 10°C to form a fraction containing the soluble periplasmic proteins (supernatant) and a residual fraction (pellet).

The activity of rPA was determined according to the method of Verheijen et al. Thromb. Haemostasis 48 (1982) 266-269).

All determined rPA concentrations in the cell extracts were standardized to cell suspensions of OD₆₀₀=1 in order to correct the error that occurs when measuring in different buffers.

A stationary overnight culture of E. coli BL21(DE3) which had been transformed with pET20b(+)-rPA and pUBS520-pIN-dnaJ (co-secretion of DnaJ) were cultured as stated in example 8. Compounds of formula I and in each case 5 mM glutathione were additionally added to the culture medium. A control culture was cultured in LB without additives. The compounds of formula I and the concentrations used are listed in table 2. The sample preparation, periplasm fractionation and the enzyme test for tPA activity were carried out as stated in example 8.

Tables 1 and 2 and figures 1 and 2 show the results of the rPA expression. Effect of L-arginine in the fermentation medium on the yield of native rPA in the periplasm Co-secreted protein 0M L-arginine 0.2 M L-arginine 0.4 M L-arginine rPA in ng/ml*OD₆₀₀ Stimulation factor rPA in ng/ml*OD₆₀₀ Stimulation factor rPA in ng/ml*OD₆₀₀ Stimulation factor - 0.030 ± 0.001 29 0.044 ± 0.090 20 0.170 ± 0.005 23 DnaJ 0.197 ± 0.019 29 0.730 ± 0.150 27 3.978 ± 1.000 18 J domain 0.339 ± 0.007 16 0.625 ± 0.213 17 4.398 ± 0.165 15 Hsp25 0.053 ± 0.002 27 0.140 ± 0.001 17 2.850 ± 0.214 17 scFvOxazolon 0.041 ± 0.003 13 0.144 ± 0.047 8 0.713 ± 0.113 10

The culture was carried out in the presence of 5 mM GSH. Effect of various low molecular weight additives in the cultivation medium on the yield of native rPA in the periplasm of E.coli Additive Concentration in the culture medium Yield of rPA in ng/ml*OD₆₀₀ in the periplasm Stimulation factor OD₆₀₀ at cell harvest Concentration of GSH in the medium without additives - 0.153 24 4.52 0 mM arginine 0.2 M 0.560 21 4.45 5 mM 0.4 M 3.880 17 1.78 5 mM formamide 0.6 M 0.208 17 4.96 5 mM 1.0 M 0.219 10 4.71 5 mM methylformamide 0.3 M 0.141 15 4.57 5 mM 0.6 M 0.790 17 1.04 5 mM acetamide 0.6 M 0.150 24 5.34 5 mM 1.0 M 1.321 16 1.57 5 mM methylurea 0.3 M 0.168 24 4.67 5 mM 0.6 M 0.830 22 4.59 5 mM ethylurea 0.3 M 0.266 23 4.20 5 mM 0.6 M 1.209 17 0.82 5 mM

A stationary overnight culture of E. coli BL21(DE3) which has been transformed with a plasmid which encodes a single chain Fv fragment of an anti-TSH antibody (US-Patent No. 5,614,367) and pUBS520 (Brinkmann et al., Gene 85 (1989) 109-114) was diluted in a ratio of 1:50 in 100 ml LB-Medium containing ampicillin (100 µg/ml) and kanamycin (50 µg/ml, Fluka Chemica, Neu-Ulm, DE) and shaken at 24°C and 170 rpm. After 3 h growth, 5 ml aliquots of the culture were added to 10 ml LB medium containing the aforementioned amounts of ampicillin and kanamycin and various concentrations of GSH (0-10 mM, Fluka) and L-arginine HCl (0-0,4 M, ICN) and each was induced with 1mM IPTG (isopropyl-β-D-thiogalactoside, AppliChem, Darmstadt). The cells were shaken for a further 21 h at 24 °C and 170 rpm and a 1 ml sample was taken after determining the OD₆₀₀. These 1 ml cell samples were fractionated in 2 ml Eppendorf reaction vessels by a modified protocol according to Jacobi et al. (J. Biol. Chem. 272 (1997) 21692-21699) (see example 8). In addition a sample of the medium supernatant (1 ml) was taken. The samples were subjected to an ELISA test to analyse them for functional antibodies.

Binding of native scFv-TSH to TSH was standardized with scFv-TSH Standard, purified with the RPAS-system (Pharmacia Biotech, Germany) (one unit corresponds to the binding of 1 µl standard to the microtiter plate coated with TSH). The addition of L-arginine to the culture medium also had a positive effect on the yield of native scFv-TSH in the periplasm and in the medium supernatant of E. coli. The addition of 0.4 M L-arginine and 5 mM GSH enabled the amount of antibody fragment that was detected by means of ELISA to be increased by 7-fold in the medium supernatant and by 43-fold in the periplasmic fraction compared to a culture with 5 mM GSH (Fig. 8).

• Allen et al., TIBS 20 (1995) 511-516
• Arrigo & Landry (1994) In Morimoto (Hrsg.): The Biology of Heat Shock Proteins and Molecular Chaperones, Cold Spring Harbour Press, 335-373
• Ausubel et al. (Hrsg.) Current Protocols in Molecular Biology, J. Wiley & Sons, 1997
• Baynex, Curr. Opin. Biotechnol. 10 (1999) 411-421
• Berges et al., Appl. Environ. Microbiol. 62 (1996) 55-60
• Bothman and Plückthun, Nat. Biotechnol. 16 (1998) 376-380
• Brinkmann et al., Gene 85 (1989) 109 - 114
• Brinkmann et al., Proc. Natl. Acad. Sci USA 89 (1992) 3075-3079
• Buchner & Rudolph, Bio/Technology 9 (1991)157-162
• Bukau, B. & Horwich, A., Cell 92 (1998) 351-366
• Ehrsperger et al., EMBO J. 16 (1997) 221-229
• EP-A 0 510 658
• EP-A 0 556 726
• Fiedler and Conrad, Bio/Technology 13 (1995) 1090 - 1093
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